Abstract Introduction: A lack of access to genetic counseling for hereditary cancer risk in rural and underserved areas is well-documented and can exacerbate disparities in cancer risk reduction and early detection. Telehealth has the potential to bridge this gap, providing remote access to specialized care. The COVID-19 pandemic accelerated telehealth availability, allowing estimation of the causal effects of shifting to a model of virtual care delivery for genetic counseling services. Methods: The Stanford Cancer Genetic Counseling Clinic provided solely in-person care at two clinical sites (Palo Alto and San Jose, CA) until March 2020, and solely virtual care from April 2020 onward. We performed a regression discontinuity design, allowing outcomes comparison before and after the threshold of early 2020, to evaluate the impact of telehealth genetic counseling on access to care for patients living in areas of higher deprivation. The assignment variable (the exposure measured before versus after the threshold) was the three-month period during which the patients were seen, with the March-May 2020 quarter excluded because of disruption of care during the early COVID-19 pandemic. The primary endpoint was proportion of patients whose primary residence zip code had a state area deprivation index of at least 4. Secondary endpoints included driving distance to the primary clinic location in Palo Alto, CA, insurance type, race/ethnicity, and primary language. Results: The study included N=5,957 patients seen in the Stanford Cancer Genetics Program between January 2017 and February 2020, and N=9,469 patients seen between June 2020 and April 2024. The regression discontinuity analysis revealed a significant discontinuity at the threshold for telehealth in access for patients living in areas of higher deprivation, who accounted for 22% of patients seen just prior to telehealth implementation and 27% just after telehealth implementation, a proportional increase of 21% (p=0.006). Mean driving distance to Palo Alto, CA also increased, from 49 minutes just prior to the threshold to 56 minutes just after (p=0.003). There were no significant differences in insurance type, race/ethnicity, or primary language across the threshold. Conclusion: The implementation of telehealth services at the Stanford Cancer Genetic Counseling Clinic significantly improved access to genetic counseling for patients from areas with higher deprivation, as evidenced by a 21% increase in the proportion of such patients among those seen. These results quantify the effectiveness of telehealth in reducing geographical and socioeconomic barriers to specialized genetic counseling and testing services. Citation Format: Jennifer L. Caswell-Jin, Hao Tang, Mina Satoyoshi, Kerry Kingham, Allison W. Kurian. Improving access to genetic counseling and testing for underserved populations through telehealth [abstract]. In: Proceedings of the 17th AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2024 Sep 21-24; Los Angeles, CA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2024;33(9 Suppl):Abstract nr C125.